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Doxycycline May Mute Painful Memories Associated With PTSD

MedicalResearch.com: What is the background for this study? What are the main findings?

Response: Posttraumatic stress disorder (PTSD) can occur after a psychological trauma such as physical violence, abuse, or natural disaster. It is characterised by increased arousal, flashbacks, and nightmares that reflect memories of the trauma. Current therapies include talking therapy, but it is costly and does not work in everybody. This is why we were looking for ways of reducing aversive memories with a drug. In the current study, we found that the antibiotic doxycycline impairs the formation of negative memories in healthy volunteers.

To form memories, the brain needs to strengthen connections between neurons. It has recently emerged that for strengthening such connections particular proteins are required that sit between nerve cells, so-called MMPs. They are involved in many disorders outside the brain, such as certain cancers and heart disease. This is how we already know that doxycycline suppresses the activity of MMPs. Since doxycycline is relatively safe and readily accessible, our research was relatively straightforward.

76 healthy volunteers – half women, half men – came to the laboratory and received either placebo (a sugar pill) or 200 mg doxycycline. They then took part in a computer test in which one screen color was often followed by a mildly painful electric shock and another color was not.

A week later, volunteers came back to the lab. They were shown the colors again , this time followed by a loud sound but never by shocks. The loud sounds made people blink their eyes – a reflexive response to sudden threat. This eye blink response was measured. Volunteers who had initially been under placebo had stronger eye blink after the color that predicted electric shock than after the other color. This “fear response” is a sensitive measure for memory of negative associations. Strikingly, the fear response was 60% lower in participants who had initially taken doxycycline.

MedicalResearch.com: What should readers take away from your report?

Response: Importantly, the idea is not to delete traumatic memories in the sense that people forget them entirely. Also, learning to fear threats is an important ability that helps us avoid danger.

To treat PTSD, it is important that traumatic memories stop scaring the patients, because the event has passed. This instinctive fear response is what doxycycline could potentially reduce.

MedicalResearch.com: What recommendations do you have for future research as a result of this study?

Response: Using drugs to prevent PTSD would of course be challenging: in the real world we rarely know when precisely a traumatic event will occur. However, there is growing evidence that people’s memories and associations may be changed after the event.

The idea is that when people actively imagine previous negative events, this makes memory brittle, and that to persist it needs to be stabilized by a process called “reconsolidation”. We are now going to test whether doxycycline will also block this reconsolidation process. If this is successful, the drug could be used to treat PTSD in a few years. To limit the use of antibiotics, we will also look into other drugs that similarly act on MMPs.

MedicalResearch.com: Is there anything else you would like to add?

Response: We have not yet tested the drug in PTSD patients, and we would not recommend using it for treatment of PTSD at this moment. We hope to be doing clinical trials in the next couple of years.

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